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Twin Turbo
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Discussion Starter · #1 ·
FML FML FML....:(

Well recently the car was running OK but had some strange issues so I thought I would attack them adn see what I could fix.
What I did...
Removed vent to atmo bov and used factory plumb back bov.
disconnected ISC and cleaned
unplugged TPS, CAS and a few other plugs and reconnected them. cleaned a few with electronic parts cleaner.
removed MAF and also cleaned with elec parts cleaner.

After re-assembling and plugging everything back in it wouldn't run properly. If i was very slow on the throttle I could get the revs up to normal but it would randomly stumble and if I reved suddenly it would also stumble.... so I cleaned the MAF again and it came good... for a week. Then same thing. Parked the car and left for a few days.
Went for a quick drive to check it and same issues then all of a sudden engine light.
Engine light pointed to Air Flow Meter.
Ordered replacement MAF. Fitted new [used] maf and the car runs fine. However still engine light. This time pointing to the above code 25.
cleared codes and re-connected old maf. car runs with issues and air flow meter code.
clear codes and fit new maf again. get code 25 again.
After this I assumed the replacement was a dud so had the seller send me another one. Fitted it tonight and same thing. cleared codes and still get code 25 after about a minute of running.


HELP....... what could cause a false code pointing to this?
 

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Twin Turbo
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Discussion Starter · #3 ·
Have checked the connections. Also tried another computer/ECU of the same part number.

Also it's a JDM 1990 GTO TT.
 

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Senior **i.e. OLD** Member
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Trying to help here....not sure what you have manual wise.....

Bob. :)
 

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Twin Turbo
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Discussion Starter · #6 · (Edited)
Currently going through the manual. On the same pages as you have posted. From what I can tell I might have some issues.
Pin 1 on harness is correct voltage.
Pin 2 on harness is earthed [but I have not disconnected the ecu like it says to do]
Pin 5 on harness is suppossed to be earthed but I get 316 ohms.

So from what I can tell I need to repair the connection between pin 5 on maf harness to pin 72 on ecu. and retest pin 2 with the ecu unplugged and see what I got.
However the manual is not very clear. Should it be open circuit from pin 2 to pin 65 or should it be earthed? ie step 3 of your 2nd pic.

Edit: from what I can gather from the pic of the multimeter it shows pin 2 to earth then earth to pin 65 so as long as pin 2 has earth and pin 65 has earth then it should be fine. So prelim testing shows it's ok.

So could a high resistance on pin 5 effect this? pin 5 is used by air flow, air temp and barro pressure.
 

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Senior **i.e. OLD** Member
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From what I read, you measure pin 2 to ground with the MAS disconnected AND with with the ECU disconnected and pin 65 of that connector grounded.

BUT, I see what you're saying....what the HELL is the GOOD reading, open or shorted????

Maybe someone else who's more awake than I am can answer that....

Bob.
 

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Twin Turbo
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5,115 Posts
Discussion Starter · #8 ·
OK I think it just clicked.... because the distance between the 2 ends of the harness are too far apart to connect each end to the multimeter the are earthing pin 65 so then whne you check continuity between pin 2 and earth it should be earthed all the way through the able via pin 65. So no earth when pin 65 is earthed means there is a break in the line somewhere. If it gets earth when pin 65 is NOT earthed then there are issues also.

Does that sound right????
 

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Senior **i.e. OLD** Member
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Yes!!!!

Why didn't they just say they were looking for a break or a short in that wire????

Bob.
 

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Twin Turbo
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Discussion Starter · #10 ·
So unless pin 65 is earthed inside the ecu somehow then I assume my wiring has issues. Looks like i'll be running new wires from pin 2 to pin 65 and pin 5 to pin 72.

PS thank you guys for taking the time to read this and help

Cheers,

Joe
 

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You should have the connector with pin 65 REMOVED from the ECU for the test.

You should see near zero ohms using the diagram provided.

If you remove the ground from pin 65 of the ECU and still see ground, then that wire (from the ECU to the MAS is shorted somewhere.

If you don't see near 0 ohms (actually you should see an open or infinite ohms) using the diagram provided (pin 65 shorted) then the wire from the ECU to the MAS is broken somewhere....

Bob.
 

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Twin Turbo
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Discussion Starter · #12 ·
Yeah I need to re-test tomorrow with the ecu unplugged.

Cheers,

Joe
 

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Senior **i.e. OLD** Member
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Gotcha....it's almost 10:30 PM your time....

I'll check the post later today (tomorrow for you :) )

Cheers!

Bob.
 

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Twin Turbo
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Discussion Starter · #14 ·
OK.... retested with the ECU unplugged and all seams fine.
Pin 2 goes direct to pin 65 with no breaks or earths. Same with pin 5. Direct to pin 72 with no breaks or earths.
So... the harness is fine and so is the computer as I swapped it out as well [unless of course the spare has the same problem :O]. So I have either got 2 dud MAFs or some other device is confusing the ECU and it's throwing this code.... what could it be?

What I might do tomorrow is pull my old MAF apart completely and de-solder it from the housing and try to clean the hot wire properly and try it again.
 

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Twin Turbo
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Discussion Starter · #15 ·
Pulled the old MAF apart. Will have a play with a few things this week. I have been trying to work out what the baromtric pressure sensor actually does. Stealth316 has this to say.

Barometric Pressure Correction
The ECU monitors the barometric pressure sensor in the mass airflow sensor (MAS). When the air pressure is low, that is at higher altitudes, ignition timing is advanced. The dsm-ecu Yahoo! email group has not found a table that performs a separate correction. The barometric pressure affects ignition timing by being included in the "air density" calculation by the ECU, which along with air volume flow and air temperature, in part, determines engine "load". Less-dense air-fuel mixtures (higher altitudes) combust slower than denser mixtures (lower altitudes) and so ignition must start earlier (timing is advanced). Though manuals state that the ignition timing advance correction is from 5º to 15º at higher altitudes, I have not seen this yet in the datalogs of my 1992 Stealth TT (I am at about 5600' ASL). Todd Day (dsm-ecu Yahoo! email group) notes that above 7500' ASL the closed loop feedback loop is tweaked, and that altitude contributes to the ECU's decision to purge the charcoal cannister and to check the EGR system for failure.
From Stealth 316 - 3S Ignition System (DOHC)

What it doesn't tell me is what happens if it's not working at all? does it just assume i'm at 0mtrs altitude? if this is the case then no issue cus I am at 0mtrs above sea level [basically anyway].
 

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Twin Turbo
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Discussion Starter · #16 ·
Bumpness... anyone? can anyone tell me what the output voltage is on pin 2 of the MAF when idling? might try to trick the ECU and just give it power at idle.

Cheers,

Joe
 

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Twin Turbo
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Discussion Starter · #17 ·
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